[PH] Lung Mechanics

compliance i.e. C = dV/dPtm

note: view picture after you answer if we were to plot the relationship of lung volume and transmural pressure difference, what would the slope be measuring?

less

note: view picture after you answer the higher the volume in a balloon, the ____ (more or less?) compliant it is?

lung becomes *less* compliant, making it harder to inflate the lung, therefore *recoil force increases*. the expansion capability of the lung is compromised, which makes it *harder to inspire air*.

note: view picture after you answer what happens to compliance and recoil force in a patient with *lung fibrosis* (i.e. restrictive lung disease)?

lung becomes *more* compliant, strengthening the obstruction particularly during expiration, making breathing more difficult because the *recoil force decreases*.

note: view picture after you answer what happens to compliance and recoil force in a patient with obstructive lung disease (i.e. significant loss of lung tissue, such as in emphysema)?

1. negative (i.e. this means inspiration is happening) 2. increase (i.e. this allows for further distension of the lung so it can cover a higher volume upon inspiration)

during *inspiration*, there is a further decrease in pleural pressure (Ppl), which exerts these two effects: 1. it produces a ___ alveolar pressure (Pa). 2. it causes transmural pressure (Ptm) to ___.

lower

the *higher* the compliance, the ___ the recoiling force.

muscle force (active force)

unlike normal expiration, *forced expiration* occurs below FRC (resting volume) and required what?

1. elastin/collagen fibers 2. surface tension

what are the 2 main factors that account for *recoiling force* of the lung?

Ppl - Pb i.e. pleural pressure - barometric outer chest surface pressure

what is the transmural pressure for the *chest wall/thorax*?

increases; decrease (i.e. more stiff)

if surface tension is *increased*, then recoiling force ___, and thus there is a ____ in compliance.

inwards; outwards

resting volume of the *lung* is far below the RV at 300mL, which can never be achieved in intact respiratory system. on the other hand, resting volume of the *chest wall* is at 60% of TLC. therefore, at FRC - the *lung* is recoiling ____ and the *thorax* is recoiling ___..

alveolar type II cells

surfactant is produced by what?

1. alveolar macrophages degrade some surfactant 2. alveolar type II cells either recycle or destroy the rest

what are the 2 mechanisms that clear components of surfactant from the surface of alveoli?

1. elasticity of the tissue 2. principle of interdependence of alveoli 3. surface tension 4. surfactant

what are the 4 factors that influence *lung compliance*?

because the pressure development in alveoli with a *small radius* is *higher* (i.e. LaPlace's Law), therefore surfactant acts to reduce this pressure in those small spaces

why is it important for surfactant to *fill the small crevices* of the alveolar surfaces?

inwards because it wants to decrease the volume

inhaling (increasing lung volume) will recoil the system in what direction and why?

if one alveolus collapses/reduces its volume, the neighboring alveoli will actually *increase* their volume and *decrease* their compliance in order to resist further expansion/collapse.

what does "interdependence of alveoli" mean if one alveolus collapses or reduces its volume?

decreases

what happens to compliance at *high* lung volumes (see lung curve)?

where transmural pressure for the chest wall (e.g. Ppl) equals zero. i.e. in the graph's case this is at 4.2 L or at 60% of TLC.

what is the *resting volume* of the chest wall, use the graph to help?

if the lung volume is *higher* than the resting volume of the chest wall

when does the *chest wall* recoil *inwards*?

if the lung volume is *lower* than the resting volume of the chest wall

when does the *chest wall* recoil *outwards*?

away

when taking a breath, do we move the respiratory system away or toward its resting volume (FRC)?

total lung capacity (TLC)

where would the *lowest* compliance be in the *lung*, given the relaxation pressure-volume curve of the lung?

1. increases (inflation of the lung becomes far easier) 2. minimizes (no air bubbles collapse in the alveoli, so fluid will move nicely from the alveolar space to the interstitium) 3. uniform (this equalizes ventilation among the alveoli based on how rapidly they are inflating)

1. surfactant *reduces* surface tension and thereby ___ lung compliance. 2. surfactant ___ (minimizes or maximizes?) fluid accumulation in alveoli. 3. surfactant helps keep alveolar size relatively ___ during the respiratory cycle.

decrease

does *surfactant* decrease or increase surface tension?

lung: would collapse reaching its resting volume (minimal lung volume below residual volume). thorax: would move outwards towards its resting volume of 60% of the TLC.

due to the *negative Ppl* in the thorax/chest wall, what would happen to the lung and thorax if there was a pneumothorax due to the alveoli air becoming accessible from the lung?

away

during *inspiration*, the *respiratory system* is moved ____ (away or toward?) its resting volume (i.e. FRC) and this requires active force of the inspiratory muscles.

toward

during *normal expiration*, the *respiratory system* is moving ____ (away or towards) its resting volume (FRC) and occurs passively without muscle force.

toward

during quiet expiration, is the respiratory system moving away or toward FRC, releasing energy?

outwards because it wants to increase the volume

exhaling (lowering lung volume) will recoil the system in what direction and why?

lung; chest wall

from a mechanical point of view, we can say that *maximal inspiration* is restricted by the ___, whereas *maximal expiration* is restricted by the ___.

air must be sucked out and the air entrance to the pleural space must be closed

how do you restore breathing to someone with a *pneumothorax*?

1. *increases* compliance 2. *decreases* collapsing tendency of alveoli 3. *decreases* the pressure difference between the alveoli, *producing alveolar stability*

if surfactant *lowers* surface tension, state what it does to each of the following: 1. compliance 2. collapsing tendency of alveoli 3. the pressure difference between alveoli

toward its resting volume (i.e. near 0 in the graph given ~300mL) because the lungs in an intact body can't be emptied below residual volume

the *lung* is always recoiling to where?

FRC

the *respiratory system* is always recoiling towards its *resting volume*, which means it is recoiling towards what?

resting volume i.e. for the respiratory system, this is FRC.

the ___ of the *respiratory system* is defined as the lung volume at which transmural pressure for the respiratory system (Pa) is equal to 0.

compliance

the relaxation pressure-volume curve of the *respiratory system* is shown in the graph given. what does the slope signify in this type of curve?

1. surfactant has a hydrophobic tail and a hydrophilic head. 2. the hydrophilic head faces the water and tries to pull surfactant into bulk flow. 3. but the hydrophobic tail faces the air and consistently counteracts the hydrophilic force, causing *surfactant to not be pulled into bulk flow*. 4. therefore, because no surfactant is being pulled into bulk flow, there is no tension on the line of surfactant molecules. i.e. think of if you were to hold hands in a circle with a group of people, if no one dives into the center there is no tension - but if 1 or 2 people dive into the middle of the circle, all the others are stretched and there is tension. - surfactant acts to prevent the diving into the middle, thus preventing tension.

what about surfactant's layout in relation to air and water causes it to produce *very little to no surface tension*, due to a small air-water interface?

Ppl - pleural pressure

what do you plot against lung volume for a relaxation pressure-volume curve of the *chest wall*?

Pa-Ppl (i.e. alveolar pressure - pleural pressure)

what do you plot against lung volume for a relaxation pressure-volume curve of the *lungs*?

Pa - alveolar pressure

what do you plot against lung volume for a relaxation pressure-volume curve of the *respiratory system*?

Pi-Po i.e. pressure on inside minus pressure on outside

what is the equation for *transmural pressure*?

Ccw = dV/dPtm = dV/d(Ppl-Pb) = dV/dPpl Pb = 0 by convention

what is the equation for compliance of the *chest wall* (Ccw)?

Cl = dV/dPtm = dV/d(Pa-Ppl)

what is the equation for compliance of the *lung* (Cl)?

Crs = dV/dPtm = dV/d(Pa-Pb) = dV/dPa Pb = 0 by convention

what is the equation for compliance of the *respiratory system* (Crs)?

1/Crs = 1/Cl + 1/Ccw

what is the equation to find the compliance of the respiratory system (Crs) using Cl (compliance of lung) and Ccw (compliance of chest wall)? note: know how to use this equation because he could ask us to find the compliance of a certain region given the other values.

to reduce the surface area to a minimum for a given volume - i.e. a higher pressure is needed to overcome force/inflation of the lung therefore, *surface tension decreases lung compliance*

what is the main property of surface tension and what affect does it have on lung compliance?

Pa - Ppl i.e. alveolar pressure - pleural pressure

what is the transmural pressure for the *lung*?

Pa - Pb i.e. alveolar pressure - barometric pressure

what is the transmural pressure for the *respiratory system*?

LaPlace's Law: P = 2 x ST/r

what law deals with surface tension to show that the *smaller the radius, the higher the inside pressure*?

lipids

what make up approximately 90% of surfactant?

its volume would increase the same as the lung i.e. they are one unit called the respiratory system in this case.

what would happen to chest cavity volume if lung volume was to increase?

FRC note: always look where the slope is the most steep, because this means the *highest* compliance since slope = compliance.

where is the *highest compliance* of the *respiratory system*? i.e. feel free to use the graph to help you understand.

50-60% of total lung capacity (TLC) note: find the steepest slope, which will equal the highest compliance.

where is the *highest* compliance of the *chest wall*? note: view picture for the relaxation pressure-volume curve of the chest wall to help answer the question.

1. Total Lung Capacity (TLC) 2. Residual Volume (RV)

where is the *lowest compliance* of the *respiratory system*? i.e. feel free to use the graph to help you understand.

residual volume (RV) note: find the smallest slope, which will equal the lowest compliance.

where is the *lowest* compliance of the *chest wall*? note: view picture for the relaxation pressure-volume curve of the chest wall to help answer the question.

the lung volume at which transmural pressure for the lung (e.g. Pa-Ppl) is equal to zero i.e. in this figure it is 300mL

where is the *resting volume* of the *lung*, use the graph to help?

below residual volume, almost at a lung volume of 0 note: you find the highest/steepest slope and that is your highest compliance since compliance = slope.

where would the *highest* compliance be in the *lung*? use the relaxation pressure-volume curve of the lung to figure out your answer.

less note: you can tell this because beyond the resting volume of the respiratory system curve, the slopes start to decrease (become more flat), which signifies less compliance

will *maximal* inspiration and expiration of the *respiratory system* be exerted against a more or less compliant respiratory system?